1. Field of the Invention
The present invention relates to an ink jet recording head and an ink jet recording apparatus provided with such recording head. More particularly, the invention relates to the structure of the element base plate (heater board) of an ink jet recording head.
2. Related Background Art
In recent years, many recording apparatuses have been used, and for these recording apparatuses, the higher recording speed, the higher resolution, the higher quality, and the lower amount of noises are demanded, among some others. Here, an ink jet recording apparatus can be cited as the recording apparatus that meets these demands.
For the typical structure and operational principle of the method used therefor, it is preferable to adopt those implemental by the application of the fundamental principle disclosed in the specifications of U.S. Pat. Nos. 4,723,129 and 4,740,796, for example. This method is applicable to the so-called on-demand type recording and a continuous type recording as well. Here, in particular, with the application of at least one driving signal that corresponds to recording information, the on-demand type provides an abrupt temperature rise beyond nuclear boiling by each of the heaters arranged corresponding to a sheet or a liquid path where ink is retained. Then, the heat generating resistive member is caused to generate thermal energy, hence creating film boiling on the thermal activation surface of a recording head to effectively form resultant bubbles in ink one to one corresponding to each driving signal. Then, by the growth and shrinkage of each bubble, liquid is discharged through each of the discharge openings, hence forming at least one droplet. The driving signal is more preferably in the form of pulses because the growth and shrinkage of each bubble can be made instantaneously and appropriately so as to attain the performance of excellent discharges of liquid, in particular, in terms of the response action thereof.
For the ink jet recording head of the kind, thermal energy is given to ink in each nozzle to create bubbles, and by means of bubbling power, ink is discharged for recording. Therefore, it is extremely important to provide the stabilization of ink discharges for the fulfillment of the aforesaid demands, and also, to control the temperature of the recording head in order to stabilize the discharging amount of ink.
To describe them more precisely, for the ink jet recording head that discharges ink by utilization of such energy as described above, the temperature of the base plate (hereinafter, may also be referred to as a heater board), where the heat generating resistive elements and the recording head wiring circuit are arranged, is influenced by the printing patterns at the time of actual printing and the environmental temperature as well. Also, depending on the temperature of the heater board at the time of driving, the time required for the application of driving signal until the actuation of bubbling is caused to be varied. As a result, the printing patterns in actual printing and the environmental temperature exert influence on the time required for the application of driving signal until the discharge is conditioned to perform an actual printing normally when the ink jet recording apparatus is driven for actual printing that begins with the status of being at rest, that is, the status of the so-called xe2x80x9cinitial discharge performancexe2x80x9d.
If the status of xe2x80x9cinitial discharge performancexe2x80x9d is unfavorable, the influence that may be exerted on the actual printing becomes greater. As means for counteracting this condition, a method is adopted to perform preliminary ink discharges before printing by applying designated driving signals prior to the execution of the actual printing. However, this means requires the consumption of ink for the operation other than the actual printing.
Under the circumstances, a control method for controlling the temperature of the heater board within a designated range is taken as an effective measure in which temperature detecting means (diode sensor) is provided for detecting temperature on the heater board where the heaters are arranged for use of ink discharges, and the heaters for use of temperature control (sub-heaters), which are arranged in the vicinity of both end portions of the arrangement of heaters for use of ink discharges, and then, on the basis of the temperature detected by temperature detecting means, the heaters for use of temperature control are driven appropriately.
On the other hand, the performance required for the ink jet recording head at present should be such as to record in the image quality in precision higher still at recording speed faster still. Further, it is desired to make such head smaller still.
Now, therefore, in order to perform recording in an image quality higher still, it is required to discharge finer ink droplets under well-conditioned control. Also, in order to record at a recording speed faster still, it is required to increase the number of heaters for use of ink discharges. Then, for the attainment of the higher precision of recorded images at the faster recording speed, it is considered effective to adopt the structure of the so-called side shooter type where ink droplets are discharged in the direction perpendicular to the heater board which is the base plate having heat generating resistive elements for use of ink discharges formed therefor. For the recording head of side shooter type, the structure is adopted so that the ink supply into the head is made from the reverse side of each heat generating resistive element of the heater board by way of the through opening that penetrates the heater board. With the structure whereby to supply ink from the reverse side of the heater board, it becomes unnecessary to make the distance between the discharge ports and a recording medium larger owing to the presence of a member for supplying ink to the head. Consequently, the degradation of impact precision of discharged ink droplets can be prevented. Also, for the recording head of side shooter type, a plurality of discharge ports can be arranged on the plane with the advantages in forming a structure in which ink droplets of plural colors should be discharged.
However, any increased number of heaters on one heater board for the implementation of higher speed recording should present itself as a cause to make the heater board larger in size. Therefore, in order to make the size of the heater board as small as possible, there is a need for reducing the number of such elements as the aforesaid diode sensors and sub-heaters other than the regular heaters. Thus, the area occupied by them on the heater board should be made the smallest possible.
Here, therefore, with the purpose of attaining the provision of image quality in higher precision at higher speed of recording, and also, making the head smaller, the inventors hereof have simply attempted to reduce the number of diode sensors and sub-heaters for the recording head of the so-called side shooter type, where, as described above, heater lines for use of discharging ink of plural colors and ink discharge ports for use of plural colors are arranged on one heater board. Then, it is found that if the number of the diode sensors and sub-heaters is simply reduced, the xe2x80x9cinitial discharge performancexe2x80x9d is degraded, and there occurs a problem that the color tone of recording images is not stabilized, among some others.
Under such circumstances, the inventors hereof have earnestly made a study to find the solution of such problems. As a result, it is ascertained that as compared with the recording head of the so-called edge shooter type where ink is discharge in the direction substantially horizontal to the heater board, these problems are encountered more conspicuously in the recording head of the side shooter mode. More precisely, it is found that in the mode of the side shooter recording head, a plurality of ink supply ports provided for the heater board demonstrate the heat insulating characteristic against the heater board material, and that this condition is the factor that should be taken into consideration when dealing with the problems described above. In other words, depending on the layout of the diode sensors and sub-heaters, the heat radiating action and the heat conduction of the heater board are deteriorated by the presence of the plural ink supply ports that shows the heat insulating characteristics. As a result, the diode sensors cannot detect the temperature of the heater board exactly or the transfer of heat generated by the sub-heaters becomes uneven on the heater board. This condition causes the initial discharge performance to be degraded or the color tone to be unstable due to the difference in temperature around each of discharge heaters used for the formation of each dot in plural colors.
As described above, there is a tendency that the discharge ports, the number of heaters arranged for one heater board, and the number of ink supply ports are increased to cope with the necessity of higher precision of recorded images at higher recording speed for an ink jet recording head. On the other hand, there is a need for making the heater board, having heater lines and ink supply ports arranged for use of plural colors, as small as possible in order to make a recording head itself lighter and smaller. Therefore, for a recording head of the so-called side shooter type where plural heater lines and ink supply ports are arranged on one heater board, it is necessary to prevent the xe2x80x9cinitial discharge performancexe2x80x9d from being deteriorated and the color tone of recorded images from becoming unstable. To this end, there should be provided means for measuring the temperature of the heater board more efficiently in accordance with the temperature characteristics obtainable by temperature detecting means, as well as means for controlling the temperature of the heater board efficiently in accordance with such measurement information.
Now, therefore, the present invention aims at the provision of an ink jet recording head of the so-called side shooter type where heater lines and ink supply ports for use of plural colors are arranged for one heater board, which has attained the higher preciseness of the quality of recorded images at higher recording speed in a smaller size of the head itself, by arranging the layout of diode sensors and sub-heaters appropriately.
In order to achieve the object of the present invention described above, the ink jet recording head of the present invention comprises a plurality of pairs arranged correspondingly on one base plate, having at least a plurality of heat generating resistive elements for use of ink discharges arranged on the base plate for generating thermal energy for discharging ink as ink droplets; a plurality of ink discharge ports each arranged in a position facing each of the heat generating resistive elements; a plurality of ink flow paths each communicated with each of the ink discharge ports; and elongated ink supply ports arranged on the base plate along the lines of the heat generating elements for use of ink discharges, being communicated with the plurality of ink flow paths. Then, on the base plate of this ink jet recording head, at least each one of means for detecting the temperature of base plate to detect the temperature of the aforesaid base plate, and means for heating base plate to heat the aforesaid base plate are arranged, and the means for heating base plate is arranged on the base plate in the vicinity of the end portion of the ink supply ports in the longitudinal direction.
Further, for this ink jet recording head, it is conceivable to arrange a plurality of means for heating base plate on the base plate. In this case, it is preferable to make the number of means for heating base plate smaller than that of the ink supply ports.
Also, it is desirable to arrange on the base plate means for heating base plate in the vicinity of both end portions of the ink supply ports in the longitudinal direction symmetrically with respect to the ink supply port positioned in the center of the plurality of ink supply ports when the plural ink supply ports are arranged in parallel. Further, it is desirable to arrange means for heating base plate on the symmetrical line of the base plate. On the other hand, it is preferable to arrange means for detecting the temperature of base plate in the vicinity of end portions in the longitudinal direction on one side of the base plate.
Also, a plurality of ink supply ports may be arranged in parallel, and means for heating base plate may be arranged on one location in the vicinity of the end portion of the ink supply ports positioned in the center of the plurality of ink supply ports on one side in the longitudinal direction. In this case, it is preferable to arrange means for detecting the temperature of base plate in the vicinity of the end portion of the ink supply ports positioned in the center of the plurality of ink supply ports on the side opposite to the side having means for heating base plate arranged thereon.
Also, for the ink jet recording head described above, the one having, on one base plate, arranged at least plural lines of heat generating resistive elements corresponding to discharge ports for use of plural colors, driving circuits for driving each line of heat generating resistive elements for use of ink discharges, and electrode portions for connecting the driving circuits with the outside is preferably suitable, and for this one, each of elongated through openings serving as ink supply ports for use of each color ink being arranged on the area excluding at least each area of the base plate having the heat generating resistive elements for use of ink discharges, driving circuits, and electrode portions arranged, respectively.
Further, for the ink jet recording head described above, the one that uses energy generated by the heat generating resistive elements for use of ink discharges to create film boiling in ink to discharge ink droplets is preferably suitable.
Also, the ink jet recording apparatus of the present invention comprises an ink jet recording head having a plurality of pairs provided at least with a plurality of heat generating resistive elements for use of ink discharges arranged on the base plate for generating thermal energy for discharging ink as ink droplets; a plurality of ink discharge ports each arranged in a position facing each of the heat generating resistive elements; a plurality of ink flow paths each communicated with each of the ink discharge ports; and elongated ink supply ports arranged on the base plate along the lines of the heat generating elements for use of ink discharges, being communicated with the plurality of ink flow paths, and a plurality of the pairs being arranged in the direction substantially perpendicular to the arrangement direction of the heat generating resistive elements for use of ink discharges corresponding to one base plate, and on the base plate, at least each one of means for detecting the temperature of base plate to detect the temperature of the aforesaid base plate, and means for heating base plate to heat the aforesaid base plate being arranged, and means for heating base plate being arranged on the base plate in the vicinity of the end portion of the ink supply ports in the longitudinal direction; a carriage for mounting the ink jet recording head thereon; and carriage scanning means for the carriage to scan in the direction substantially in parallel to the arrangement direction of the aforesaid plural pairs.
With the side shooter type recording head structured as described above, it is compatible to form images in high precision and to attain a high printing speed. Conceivably, therefore, a plurality of ink supply ports are provided for one heater board. Then, for example, it becomes possible to implement the bidirectional printing without color unevenness by arranging plural ink supply ports for one and the same color ink in the head scanning direction.
With the structure having a plurality of elongated ink supply ports, it becomes possible to keep the temperature distribution on the base plate as uniform as possible in the arrangement direction of ink supply ports with the minimum sub-heater number without causing the heat transfer to be impeded by the presence of a plurality of ink supply ports and many numbers of heat generating resistive elements for use of ink discharges by arranging means for heating base plate (sub-heater) in the vicinity of end portion of the ink supply ports on the base plate in the longitudinal direction. In this way, the xe2x80x9cinitial discharge performancexe2x80x9d can be kept in good condition, while making the temperature difference smaller on the circumference of each heat generating resistive element for use of ink discharges to form each of the recording dots for representation of plural colors, hence making it possible to record with stabilized color tones.
Also the layout of the sub-heater that can maintain the uniformity of the temperature distribution of the base plate makes it possible to reduce the arrangement number of the means for detecting the temperature of the base plate which is provided for the base plate to control the base pate temperature. Further, this layout enables the degree of freedom to be widened for the arrangement locations thereof. Thus, the size of the base plate can be made as small as possible even if the number of elements and wiring circuits are increased on the base plate along the intended attainment of higher preciseness of the quality of image formation.
As has been described, when designing a heater board, it is made possible to arrange elements more effectively so as to provide an ink jet recording head which is not only excellent in productivity at lower costs, but also, in the implementation of higher saving of power dissipation.